Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $85.62   8.360%   $92.7778   $92.78   $92.80   $92.80  
  Purchase #2 $11.93   13.696%   $13.5639   $13.56   $13.55   $13.60  
  Purchase #3 $53.99   8.535%   $58.598   $58.60   $58.60   $58.60  
  Purchase #4 $142.84   8.126%   $154.4472   $154.45   $154.45   $154.40  
  Purchase #5 $70.65   8.793%   $76.8623   $76.86   $76.85   $76.90  
  Purchase #6 $217.98   9.429%   $238.5333   $238.53   $238.55   $238.50  
  Purchase #7 $55.94   9.285%   $61.134   $61.13   $61.15   $61.10  
  7 purchase totals = $638.95       $695.9165   $695.91   $695.95   $695.90